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LTC6813 cell balancing issue

Category: Hardware
Product Number: LTC6813-1

Hi,

I'm using the LTC6813-1 with isoSPI and 16 cells in the stack. C12 and C18 are connected to the battery stack through a 100 ohm resistor as recommended in the datasheet as per Fig.47. Cell connection schemes for 16 and 14 cells. I'm facing an issue with the cell balancing and cell measurement on the LTC6813-1. Inititally when I run a code for only cell measurement, I can read all the cell voltages correctly as given below:

C1:3.663700,C2:3.690800,C3:3.676900,C4:3.698400,C5:3.677000,C6:3.699400,C7:3.676500,C8:3.689000,C9:3.666600,C10:3.700800,C11:3.677200,C12:0.000000,C13:3.685000,C14:3.685800,C15:3.677200,C16:3.697600,C17:3.639200,C18:0.000000

However after i enable cell balancing once of every alternative cell and then disable cell balancing, the S pins of different cells are not turning off. The cell voltages of some cells are then completely wrong as the  gate-source voltage of few of the external p-channel mosfets are ~2.7V. I'm using the external balancing circuit with p-channel mosfets and 18E balance resistor.
After this with even all the S pins off and DCP disabled, the cell voltage readings are given as follows:

C1:3.635300,C2:3.650700,C3:3.645200,C4:3.682400,C5:3.666900,C6:3.683100,C7:3.665500,C8:3.676300,C9:3.594600,C10:3.676300,C11:3.667000,C12:0.000000,C13:3.652200,C14:3.667000,C15:4.148000,C16:3.926000,C17:1.449300,C18:0.971500

C15, C16 and C17 and C18 cell voltages are wrong and i've even verified with a DMM that these are the voltages being seen at C15, C16, C17 and C18 on the board. However before the balancing circuit at the cells, the voltages are correct with all cell voltages at ~3.6V.

What could be the reasons for this issue?